Breakdown of heavy quasiparticles in a honeycomb Kondo lattice: A quantum Monte Carlo study

TL;DR

This study uses quantum Monte Carlo simulations to show that in a honeycomb Kondo lattice, heavy quasiparticles break down at small Kondo couplings within the magnetic phase, revealing a decoupling of magnetic transition and quasiparticle coherence.

Contribution

It provides the first explicit example of Kondo breakdown within the magnetically ordered phase on a honeycomb lattice using quantum Monte Carlo methods.

Findings

Kondo breakdown occurs at small J_k in honeycomb lattice.

Heavy quasiparticles become incoherent at small J_k.

Magnetic transition and quasiparticle breakdown are decoupled.

Abstract

We show that for the half-filled Kondo lattice model on the honeycomb lattice a Kondo breakdown occurs at small Kondo couplings $J_k$ within the magnetically ordered phase. Our conclusions are based on auxiliary field quantum Monte Carlo simulations of the so-called composite fermion spectral function. Within a U(1) gauge theory formulation of the Kondo model, it becomes apparent that a Higgs mechanism dictates the weight of the resonance in the spectral function. For the honeycomb lattice we observe that for small $J_k$ the quasiparticle pole gives way to incoherent spectral weight but it remains well defined for the square lattice. Our result provides an explicit example where the magnetic transition and the breakdown of heavy quasiparticles are detached as observed in Yb(Rh$_{0.93}$Co$_{0.07}$)$_2$Si$_2$ [Friedemann et al., Nat. Phys. \textbf{5}, 465 (2009)].